A typical six wheel truck assembly is shown in FIG. 1 of U.S. Pat. No. 5,242,131 to Watts issued Sep. 7, 1993 and also assigned to the Boeing Company the details of which are incorporated herein by reference. Watts, U.S. Pat. No. 5,242,131 titled "Steerable Landing Gear", is illustrative of reduced landing gear turning forces on an airplane with a six wheel, three axle truck. Tire scrubbing, and hence tire wear, is reduced by a steerable axle on either the rear, or both forward and rear positions on the truck. The axle is operated by two hydraulic actuators proportionally controlled by the nose gear steering system. In contrast the present improvement defines the rear axle actuation mechanism comprising a "walking beam" mechanism operated by a single, center-locked hydraulic actuator, positioned between the center and rear (or front) axles. A compact, minimum weight installation is achieved, which does not compromise airplane towing or jacking. Also, U.S. Pat. No. 5,242,131 shows that attachment of the hydraulic components aft of the axle vertical plane do not facilitate conventional towing and jacking attachments.
Further exemplary prior art includes U.S. Pat. No. 2,538,388 to Sievers and U.S. Pat. No. 3,091,416 to Knight et al. which are intended to position a main landing gear for cross-wind landing operations. U.S. Pat. No. 2,538,388 also has a steering function but requires an externally-driven torque shaft, internal to the shock strut, powering a spur gear on the underside of the truck beam. This gear engages with exposed gearing and link mechanisms to steer multiple wheel pairs. U.S. Pat. No. 2,851,231 to Wescott is limited to a tandem wheel configuration. The forward truck beam 17 is connected directly to the airplane by torque links 27. The rear truck beam 16 is integral to the shock absorber inner cylinder and is free to caster during steering maneuvers. It is aligned (for retraction) by an inner cylinder cam 44 engaging a centering cam 43, when the shock strut extends fully on takeoff. U.S. Pat. No. 3,904,153 to Watts also assigned to the Boeing Company defines an entire nose landing gear with mechanisms for gear actuation, locking and steering.